Cyanide electroplating baths and processes



United States Patent M 3,296,101 CYANIDE ELECTROPLATING RATES AND PROCESSES James R. Crain, Penn Hills, Pa., assignor, by mesne assignments, to Cowles Chemical Company, Shaker Heights, Ohio, a corporation of Ohio N0 Drawing. Filed Feb. 25, 1963, Ser. No. 260,823 19 Claims. (Cl. 204-44) This invention relates to the deposition of metals from cyanide metal plating baths and has particular reference to novel electrotyles and processes associated therewith which will produce brighter and smoother metal electrodeposits.

Numerous compounds, singly and in combination, are employed as additives -in the cyanide electrolytes from which metals such as copper, brass, bronze, zinc, cadmium, gold and silver are deposited. The problems of obtaining satisfactory electrodeposits are manifold. Deposits of metal are frequently required to possess one or more properties such as brightness, ductility, refined grain, smoothness and attractive color. Moreover, in the plating process, it is desirable to obtain the desired properties over a substantial current density range. Compounds which improve one or more of these properties of the electrodeposited metal or which provide advantages in the plating process are added to the electrolyte solutions either singly or in combination with other additives.

Accordingly, it is the general object of this invention to provide novel cyanide electrolyte plating baths and processes associated therewith capable of enhancing the brightness, color and smoothness of the electrodeposited metal.

A more specific object of this invention is to provide novel cyanide electrolyte plating baths containing soluble salts derived from the reaction of certain substituted and unsubstituted thioltriazines with certain substituted and unsubstituted primary and secondary amines so that the brightness, color and smoothness of the metal is enhanced over a relatively broad range of current densities.

Yet another object of this invention is to provide novel cyanide electrolyte plating baths containing soluble salts derived from the reaction of certain substituted and unsubstituted thioltriazines with certain substituted and unsubstituted primary and secondary amines in combination with certain polymerized alkyl naphthalene sulfonic acids so that the brightness, color and smoothness of the metal is enhanced over a relatively broad range of cur rent densities for prolonged periods of electrolyte use.

Other and further objects of this invention will, in part, be obvious and will, in part, appear hereinafter.

Briefly, this invention comprises the addition of cert-ain compounds to conventional cyanide electrolyte plating baths to promote brighter and smoother deposits of the metal. These addition agents are the soluble salts derived from the reaction of certain substituted and un substituted thioltriazines with certain substituted and unsubstituted primary and secondary amines either alone or in combination with certain polymerized alkyl naphthalene sulfonic acids.

In accordance with this invention and in the attainment of the foregoing objects, it has been discovered that the brightness, smoothness, and leveling of metals deposited from cyanide electrolytes is improved by the addition to Patented Jan. 3, 1967 the electrolyte of water soluble brightner compounds prepared by reacting (A) at least one compound having the formula:

wherein R is -a radical selected from the group consisting of hydrogen, thiol, amino and hydroxyl radicals with (B) at least one compound having the formula:

\NH Rf wherein R and R are radicals selected from the group consisting of (1) hydrogen, (2) substituted and unsubstituted aliphatic radicals containing not more than four carbon atoms in which the substituents are selected from the group consisting of -NH Cl, OH and SO Na, (3) substituted and unsubstituted alicyclic radicals containing from 4 to 6 carbon atoms in which the substituents are selected from the group consisting of NH -C1, -OH and SO Na and (4) substituted and unsubstituted heterocyclic radicals containing 5 to 6 ring atoms selected from the group consisting of C, S, N and O atoms at least three of which are C atoms and in which the substituents are selected from the group consisting of NH -C1, OH and SO Na.

Examples of suit-able compounds described by the Formula A hereinabove, referred to hereinafter as thiotriazine compounds for convenience, include dithioarnmelide, dithiocyanuric acid, 2-rnethyl-s-triazine-4-6-dithiol, 2,4-s-triazinedithiol and trithiocyanuric acid.

Examples of compounds which may be employed in the reaction with the described thio-triazine compounds include methylalomine, 2-chloroethylamine, 1,4-diaminobutane, ethylarnine, the sodium salt of 3-amino-n-propylsulfonic acid, methylethylamine, (arninoethyl) ethylamine, dietha-nol-amine, methylhydroxymethylamine, di- (chloropropyl) amine, aniline, chloroaniline, p-aminoaniline, 3-hydroxycyclopentylamine, 3-aminobenzenesodiumsulfonate, diphenylamine, 2 -hydroxycyclobutenyl phenyl amine, methyl phenyl amine, 3-hydroxyethylaminobenzene sulfonic acid sodium salt, di(p-aminophenyl) amine, chloromethylaniline, diethylenetriam'ine, Z-aminothiazole, pyridine, pyridine-3-sulfonic acid salt, Z-methylaminopyrrole, S-aminopyridine, 2,4-dihydroxypyridine, Z-amino-S-chlorofuran, 3,5-dichloropyridine, and guanidine. It is apparent that these compounds are described by the Formula B hereinabove. For convenience, these compounds will be referred to hereinafter as the amino compounds.

The described amino compounds are sufliciently strong bases so that they will react with the hydrogen of the thiol radical of the thiol-triazine compound to form a salt therewith. It is apparent that the described thioltriazine compounds may contain two or three thiol groups. One to three moles of the amino compounds may be employed to react with the thiol groups.

Obviously, in products resulting from the reaction of amines with these thioltriazines all of the thiol groups 'mula.

arenot necessarily reacted. If, for example, only one mole of an amine is reacted with trithiocyanuric acid it is apparent that all of the thiol groups would not be reacted.

It is to be understood that dithioammelide exists as an intromolecular salt. The amine group of the dithioammelide is basic enough to react with a thiol group on another molecule of dithioammelide. The formula outlined hereinabove in the case of dithioammelide then, should be considered to be an empirical formula, the intramolecular salt being a dimer or polymer of this for- Obviously, in this intramolecularsalt', only one thiol group of the dithioammelide is available for further reaction with an amine.

While other reaction mediums for the preparation of the brightener compounds may be employed, either water and/ or lower alkyl alcohols having up to 4 carbon atoms are preferred as the solvent or reaction medium. Alkylolamines are the preferred amino compounds because they produce brightener or salt compounds which are among the most soluble.

These water soluble salt compounds, which are employed in this invention as brighteners in metal cyanide electrolytes, and the processes for preparing these salt compounds, are disclosed and claimed in U.S. application Serial No. 260,896 filed February 25, 1963, which is assigned to the assignee of this invention. Reference is made thereto for details and specific examples of the preparation of these compounds. It is to be understood that for convenience, these water soluble salts may be referred to as reaction product additives.

The thioltriazine compounds, described as reactants in detail heretofore, may also be described as thiol substituted heterocyclic ring compounds in which the ring members comprise alternating carbon and nitrogen atoms, in which at least two of the ring carbons carry a thiol substituent. As described hereinabove, the amino compound will, according to this invention, react with at least one of the thiol substituents to produce a salt therewith. Thus, the salt products of this invention may be described as water soluble substituted heterocyclic ring compounds in which the ring members comprise alternating carbon and nitrogen atoms in which at least one ring carbon carries a substituent having the general formula:

\NHPS- R wherein R and R are radicals selected from the group consisting of (1) hydrogen, (2) substituted and unsub stituted aliphatic radicals containing not more than four carbon atoms in which the substituents are selected from the group consisting of NH Cl, OH and SO Na, (3) substituted and unsubstituted alicyclic radicals containing from 4 to 6 carbon atoms in which the substituents are selected from the group consisting of NH Cl, OH and SO Na and (4) substituted and unsubstituted heterocyclic radical containing 5 to 6 ring atoms selected from the group consisting of C, S, N and O atoms at least three of which are C atoms and in which the substituents are selected from the group consisting of NI-I Cl, OH and SO Na. It is to be understood, of course, that other ring carbon atoms may also be so substituted or they may carry a radical selected from the group consisting of hydrogen, methyl, amino, hydroxyl and thiol radicals. In any event, at least 2 carbon atoms shall be bound to sulfur atoms.

It has also been discovered that the brightness of a metal deposited from the described cyanide electrolyte may be even further enhanced by also adding organic materials such as the sodium and potassium salts of polymerized alkyl naphthalene sulfonic acids. These auxiliary brighteners may be described as the sodium and potassium salts of compounds having the formula:

SO H $03K 11 wherein R is selected from the group consisting of methyl and ethyl radicals and n is from 1 to about 100. The use of the polymerized alkyl naphthalene sulfonic acids, in conjunction with other compounds, is disclosed, for example, in U.S. Patents 2,701,234, 2,774,728, 2,841,542, 2,861,929 and 2,970,951. In conjunction with the described reaction product brightener compounds, the auxiliary brightener also increases the bright current density range, improves anode corrosion so that less anode polarization occurs and prolongs the active life of the brightener compound. These compounds may be referred to as auxiliary additives, for convenience.

In order to indicate even more fully the advantages and capabilities of the present invention, the following specific examples are set forth to illustrate the utilization of the reaction product additive brightener compounds and auxiliary additive brightener compounds in cyanide metal plating baths.

Example I An aqueous electroplating electrolyte of the following composition was prepared:

Reaction product of dithioammelide and 2-aminoethanol 0.008

This bath was operated at a temperature of 165 F. with air agitation. Copper was plated on rectangular steel panels from the bath using a periodic reverse current having a plate time of 5 seconds and a deplating time of 1 second, the reverse current being of the plating current. An excellent smooth and bright copper deposit was obtained over a current density range up to 100 a.s.f. Increasing the amount of the reaction product to 0.02 oz./gal. in the bath resulted in bright deposits over a current density range up to 90 a.s.f. Panels plated from the bath using interrupted direct current and direct cur,- rent methods showed a bright range up to 50 a.s.f.

Example II An aqueous bath of the following composition was operated at F. with air agitation to plate steel panels.

Oz./gal. Copper 6.0 KOH 5.0 Free KCN 1.2

Reaction product of dithioammelide and Z-aminoethanol 0.01 Sodium salt of polymerized naphthalene bis-sulfonic acid 0.006

Example III An aqueous bath of the following composition was operated at C. to plate steel panels using a periodic reverse current process having a plating time of 60 seconds and a deplating time of 40 seconds, the reverse current being 50% of the plating current.

Reaction product of dithioammelide and 2-aminoethanol Sodium salt of polymerized naphthalene bis-sulfonic acid 0.006

Thisbath produced excellent bright leveled copper deposits.- The same bath without the reaction product and the sodium salt produced a hazy bright deposit.

Example IV Aqueous baths of the following compositions were em ployed in a series of tests in a Hull Cell with additives known in the art and an additive of this invention at various concentrations of each. All of the baths were operated at 180 F. with air agitation.

Oz./gal. Basic bath:

Copper 6.0 Free KCN 1.2 KOH 5.0 Additives to basic'bath:

1A. Diethiommelide 0.005 1B. Dithioammelide 0.005

Z-aminoet-hanol 0.002

1C. Reaction product of dithioammelide and 2'-aminoethanol "110.005 2A. Dithioammelide 0.05 23. Dithioammelide g 0.05 Z-aminoethanol 0.04

2C. Reaction product of dithioammelide and Z-aminoethanol 005 3A. Dithioammelide 0.10 SE. Dithioammeliden; 0.10 Z-aminoethanol 0.04

3C. Reaction product of dithioammelide and 2-aminoethanol 0.10

TABLE I.-BRIGHI CURRENT DENSITY RANGES ON HULL CELL PANELS IN A.S.F.

Additive System PR Panels DC Panels 35-120 -35 0-70 0-20, 70-140 0-120 38-80 0-20, 55-130 0-10, 30-110 0 0-20, 40-80 0-130 a.s.f. 0-18, 36-110 0-15, 55-140 0-18, 60-130 0-15, 55-140 0-18, 60-130 0-140 0-30, 50-130 It is apparent from the data presented in Table I that the brightness and current density ranges from the baths containing the reaction product additive are superior to the bat-hs containing dithioammelide alone or the unreacted dithioammelide in combination with 2-aminoethanol.

Example V An aqueous bath of the following composition was operated at 165 F. with air agitation to plate Hull Cell panels at 3 amperes using the periodic reverse current cycle described in Example IV.

Oz./ gal. Copper 6.0 Free KCN 1.2

KOH 5.0

NaCNS 0.4

ZnO 0 06 Reaction product of dithiocyanuric acid and methylchloroaniline 0.01

A bright copper deposit was obtained in a current density range of 0-130 a.s.f. Increasing the reaction product concentration to 0.2 oz./ gal. shortened the bright current density range to 0-100 a.s.f.

Example VI An aqueous bath of the following composition was operated at 180 F. to plate Hull Cell panels using the periodic reverse current cycle described in Example IV.

Oz./gal.

Copper 6.0

Free KCN 1.2

KOH 5.0 Reaction product of trithiocyanuric acid and dimethylamine- 0.015

A bright copper deposit wasobtained in a current density range of 0-50 a.s.f. Adding 0.06 oz./gal. of ZnO and 0.01 oz./ gal. of the potassium salt of polymerized naphthalene bi-sulfonic acid enhanced the brightness and increased the range to 0-110 a.s.f. No appreciable benefit was noted from further additions of the reaction product.

' Example'VII An aqueous bath of'the following composition was operate'd'at F. with air agitation of plate Hull Cell panels employing an interrupted direct current.

A bright range of 0-85 a.s.f. was observed on the panel. Adding 0.002 0z./ gal. of the sodium salt of polymerized naphthalene bis-sulfonic acid enhanced the brightness but the bright current density range was reduced to 0-75 a.s.f.

Example VIII An aqueous bath of the following composition was operated at F. with air agitation to plate Hull Cell panels employing the period reverse cycle of Example IV.

Oz./ gal. Copper 8.3 Free NaCN 2.0 NaOH 4.0 Na C O 10.1

Reaction product of trithiocyanuric acid and methylethanolamine 0.008

A bright range of about 0-100 a.s.f. was observed on the panel. The addition of the sodium salt of polymerized napthalene bis-sulfonic acid produced a sample with more depth of color in the bright range.

Example IX This example was identical to Example VIII, except that 0.015 oz./ gal. of the reaction product of s-triazine- 2,4-dithiol and n-butylamine was employed as the brightener. Results substantially identical to that of Example VIII were observed.

Example X An aqueous bath of the following composition was operated at 100 F. at room temperature to plate Hull Cell panels employing a periodic reverse current having a plating time of 20 seconds and a deplating time of 2 seconds, the reverse current being 100% of the plating current.

A bright range from to 100 a.s.f. was observed on the panel of deposited white brass. It was also observed that the white brass anodes were brightened, resulting in better anode corrosion. Addition of 0.003 oz./gal. of the sodium salt of polymerized naphthalene bis-sulfonic acid produced brighter deposits from 0-120 a.s.f.

In aqueous baths and processes identical to that described in Example 1X except that another reaction product was employed, substantially equivalent results were obtained with the reaction product of dithiocyanuric acid and sodium aminobenzene-sulfonate.

At least 0.005 ounce of the reaction product additive compound should be added for each gallon of the aqueous metal cyanide bath, preferably from 0.008 to 0.2 ounce per gallon of bath. At least 0.001 ounce of the auxiliary brightener should be added for each gallon of the bath when the combined reaction product and auxiliary brightener system is to be employed. The maximum concentration of either the reaction product additive or the auxiliary additive is limited only by the solubility of the particular compound in the bath. With high concentration of the auxiliary additive, a striated deposit of metal may be produced. These striations can be eliminated by increasing the free cyanide content of the bath.

The described reaction product additives and the described auxiliary additives may be used in further combination with other known additives for cyanide electroplatingbaths, as for example together with zinc oxide and sodium thiocyanate. This particular combination provides a particularly prolonged active life for the brightener compounds.

Aqueous alkaline metal cyanide electroplating baths are well-known in the art. Metals which fall within the scope of this invention include, for example, copper, brass and zinc. The aqueous cyanide plating baths will contain soluble compounds of at least one of the metals selected from the group consisting of copper and zinc. The makeup of these baths is disclosed in the patent literature and also in standard texts or handbooks, as for example the Metal Finishing Guidebook Directory, 30th Ed.,'1962,

published by Metals and Plastics Publications, Inc., West-' wood, New Jersey.

While the present invention has been described with particular reference to preferred embodiments thereof, it will be understood, of course, that certain changes, substitutions, modifications and the like may be made therein without departing from its true scope.

I claim as my invention:

1. An aqueous alkaline cyanide metal plating solution containing a metal cyanide from the group consisting of copper cyanide and mixtures of copper cyanide and zinc cyanide, an alkali cyanide and an eifective amount sufficient to impart brightness of Water soluble salt formed from (A) at least one compound having the =forn'1ula 8 wherein R is a radical selected from the group consisting of hydrogen, thiol, amino and hydroxyl radicals and (B) at least one compound having the formula wherein R and R are radicals selected from the group consisting of (1) hydrogen, (2) substituted and unsub stituted aliphatic radicals containing not more than four carbon atoms in which the sub'stit'uents are selected from the radicals consisting of -NH -Cl, -OH and SO Na, (3) substituted and unsubstituted carbocyclic radicals containing from 4 to 6 ring carbon atoms in which the substituents are selected from the radicals consisting of --NH Cl, OH and S0 Na and (4) substituted and unsubstituted heterocyclic radicals containing 5 to 6 ring atoms selected from the, group consisting of C, S, N and O atoms at least three of which are C atoms and in which the substituents are selected from the group consisting 0f'-NH Cl, -OH and SO Na.

2. An aqueous alkaline cyanide metal plating solution containing a' metal cyanide firom the group consisting of copper cyanide and mixtures of copper cyanide and zinc cyanide, an-alkali cyanide and an effective amount suffi-cient to impart brightness of water soluble salt formed from (A) at least one compound selected from the group consisting of dithi-ocyanuric acid, dithioammelide, Z-methyl-s-triazine-4,6-dithiol, 2,4-s-triazinedithiol and trit'hiocyanuric acid and (B) at least one compound selected from the group consisting of methyl-olamine, Z-aminoethanol, 2-chloroethylamine, 1,4-diaminobutane, ethyla1mine,'the sodium salt of 3-amino-n-prcpylsulfon1'c acid, methylethyl'amine, (aiminoet-hyl) ethylamine, diethylolamine, rnethylhydroxy-met'hylamine, di(chloropropyl)- amine, aniline, chl-oroaniline, p-aminoaniline, 3-hydroxycyclopentylamine, phenyl-amine, Z-hydroxycyclobutenyl phenylamine, methyl phenyl amine, 3-hydrcxyethylaminobenzene sulfonic acid sodium salt, -di(p-aminophenyl)amine, chlorometlr,

wherein R is a radical selected from the group consisting of hydrogen, thi'ol, amino and hydroxyl radicals and (B) at least one compound having the formula wherein R and R are radicals selected from the group 3-arninobenzenesodiumsulfionate, di-.

9 consisting of (1) hydrogen, (2) substituted and unsubstituted aliphatic radicals containing not more than four carbon atoms in which the substituents are selected from the radicals consisting of. NH;;, Cl, OH and AO Na, (3) substituted and unsubstituted carbocyclic radicals containing from 4 to 6 ring carbon atoms in which the substituents are selected irom the radicals consisting of NH;,, Cl, OH and SO Na and (4) substituted and unsubstituted heterocyclic radicals containing 5 to 6 ring atoms selected from the gnoup consisting of C, S, 10

N and O atoms at least three of which are C atoms and in which the substituents are selected from the group consisting of NH -Cl, OH and SO Na.

4. The aqueous alkaline cyanide metal plating solution of claim 1, in which at least 0.005 ounce of the added compound is dissolved per gallon of solution.

5. The aqueous alkaline cyanide metal plating solution of claim 1, in which from 0.008 to 0.2 ounce of the added compound is dissolved per gallon of solution.

6. The aqueous alkaline cyanide metal plating solution of claim .1, also containing an auxiliary hrightener selected trom the group of sodium and potassium salts of compounds having the tormula:

new

$03K S0311 11 wherein R is selected from the group consisting of methyl and ethyl radicals and n is irom 1 to about 100.

7. The aqueous alkaline cyanide metal plating solution of claim 6, containing at least 0.001 ounce of the auxiliary brightener per gallon of solution.

8. The aqueous alkaline cyanide metal plating bath of claim 1 in which the metal of the metal cyanide is copper.

9. The aqueous alkaline cyanide metal plating bath of claim 1 in which a mixture of copper and zinc cyanides is used.

10. The aqueous alkaline cyanide metal plating solution of claim 2, in which at least 0.005 ounce of the added compound is dissolved per gallon of solution.

11. The aqueous alkaline cyanide metal plating solution of claim 2, also containing an auxiliary bri-ghtener added compound is dissolved per gallon of solution.

12. The aqueous alkaline cyanide metal plating solution of claim 2, also contaning an auxiliary brightener selected from the group of sodium vand potassium salts of compounds having the fonmula:

wherein R is selected from the group consisting of methyl and ethyl radicals and n is from 1 to about 10 0.

13. The aqueous alkaline cyanide metal plating solution of claim 12, containing at least 0.001 ounce of the auxiliary hrightener per gallon of solution.

14. The aqueous alkaline cyanide metal plating bath of claim 2 in which the metal of the metal cyanide is copper.

15. The aqueous alkaline cyanide metal plating bath of claim 21in which a mixture of copper and zinc cyanides is used.

1 6. The aqueous alkaline cyanide metal plating bath of claim 2 in which the water soluble compound is the product of the reaction of dithioammelide and Z-aminoethanol.

17. The aqueous alkaline cyanide metal plating bath of claim .2 in which the water soluble compound is the product of the reaction of trithi-ocyanuric :acid and methylethanolamine.

18. The aqueous alkaline cyanide metal plating bath of claim 2 in which the water soluble compound is the product of the reaction of dithiocyanuric acid and methylchloroaniline.

19. The aqueous alkaline cyanide metal plating solution of claim 12 also containing zinc oxide and sodium thiocyanate.

References Cited by the Examiner UNITED STATES PATENTS 2,609,339 9/1952 Passal 20452 2,774,728 12/ 1956 Wernlund 20452 2,841,542 7/l958 -Manquen 20 4-52 2,849,352 8/1958 Kirsta hler et :al. 20444 2,862,861 12/1958 Moy 20452 2,970,951 2/ 1961 Manquen et al 20452 3,018,232 l/l962 Bishoff et a1. 20444 JOHN H. MACK, Primary Examiner.

G. KAPLAN, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,296,101 January 3, 1967 James R. Crain e above numbered t error appears in th should It is hereby certified the that the said Letters Patent patent requiring correction and read as corrected below.

Column 5, before line 2, insert the following ingredient:

elide" read for "bi-sulfonic" line 27, for "Diethiomm column 6, line 28,

same column 5,

line 36, for "of" read to Dithioammelide read bis-sulfonic Signed and sealed this 3rd day of October 1967 (SEAL) Attest:

EDWARD J BRENNER ERNEST W. SWIDER Attesting Officer Commissioner of Patents 

1. AN AQUEOUS ALKALINE CYANIDE METAL PLATING SOLUTION CONTAINING A METAL CYANIDE FROM XXX GROUP CONSISTING OF COPPER CYANIDE AND MIXTURES OF COPPER CYNIDE AND ZINC CYANIDE, AN ALKALI CYANIDE AND AN EFFECTIVE AMOUNT SUFFICIENT TO IMPART BRIGHTNESS OF WATER SOLUBLE SALT FORMED FROM (A) AT LEAST ONE COMPOUND HAVING THE FORMULA 